1. Field of the Invention
The present invention relates to a coil for magnetic resonance imaging (MRI) technology and, particularly, to a birdcage multi-channel body coil.
2. Description of the Prior Art
In the conventional designs of multi-channel body coil, a birdcage coil is of a design which is simple and has been widely used. FIG. 1 is a schematic view of an existing birdcage multi-channel body coil. As shown in FIG. 1, the birdcage multi-channel body coil generally is in a cylindrical shape, comprising eight coil units 101 connected in succession in the circumferential direction along the side faces of the cylinder, usually the eight coil units 101 are of the same size. Of course, what is shown in FIG. 1 is only for exemplary illustration, in practical applications the number of the coil units 101 can be disposed according to practical requirements.
The birdcage multi-channel body coil is able to generate a uniform radio frequency field which no other multi-channel body coils can match. However, by adopting this style of design, the field generated by one of the coil units will influence the field generated by the other coil units, that is to say, there is coupling between different coil units in the birdcage multi-channel body coil, thus affecting the signal transmitted and received during scanning. For this reason, in the prior art the Butler Matrix circuit technology is generally adopted to solve this problem. That is, the signals collected by the birdcage multi-channel body coil are processed by a single Butler Matrix circuit and then they are emitted as an output.
Due to the existence of the coupling, there are multiple modes mixed together in the signals collected from each channel by the birdcage multi-channel body coil, causing an inhomogeneous field, therefore, in the Butler Matrix circuit technology, the frequency spectrum of signals is obtained by the method of Fourier transform, and then the receipt of the signal of a single mode is accomplished, so as to overcome the influence of the coupling. However, the hardware implementation of the Butler Matrix circuit technology is very complicated, which is very inconvenient in practical applications.